Vehicles using an engine, which uses gasoline, diesel oil, and the like as an energy source, as a driving source are a general vehicle type. However, the vehicles increasingly require new energy sources due to various factors such as the environmental pollutions of the energy sources for vehicles and the reduction in oil deposits. At present, one of technologies which are the closest approach to commercialization drives vehicles using a fuel cell as an energy source.
However, unlike the existing vehicles having an engine using petroleum as an energy source, vehicles using the fuel cell may not use a heating system using cooling water. That is, the existing vehicles having the engine using petroleum as an energy source have considerable heat generated from the engine, include a cooling water circulation system for cooling the engine, and allow the cooling water to use heat absorbed from the engine for indoor heating. However, since driving sources used in the vehicles using the fuel cell do not generate heat as much as that generated from the engine, the electric vehicles have a limit of using the existing heating scheme.
Therefore, various researches for fuel cell vehicles having a heat pump added to an air conditioning system, using the heat pump as a heat source, and including a separate heat source such as an electric heater, or the like have been conducted.
As the related technology, Korean Patent Laid-Open Publication No. 10-2012-0103054 (Published on Sep. 19, 2012, Title: Heat Pump System For Vehicles) is disclosed. FIGS. 1 and 2 are configuration diagrams illustrating the existing vehicle heat pump system.
As illustrated in FIGS. 1 and 2, the vehicle heat pump system 10 mainly includes an outdoor heat exchanger 11, an indoor heat exchanger 12, an evaporator 13, a compressor 14, an expander 15, and a chiller 16.
First, a heating cycle will be described with reference to FIG. 1. The indoor heat exchanger emits high-temperature heat during the heat exchange of a high-temperature and high-pressure refrigerant and supplies the emitted heat to the interior of the vehicle, thereby heating the interior of the vehicle.
The refrigerant having passed through the indoor heat exchanger passes through a first valve 21 and then passes through the chiller 16 by a second three-way valve 23 without passing through the outdoor heat exchanger by a first three-way valve 22 to exchange heat with cooling water for electrical parts introduced from an electric radiator 24, such that the chiller serves as an evaporator. Thereafter, the refrigerant repeatedly passes through a circulation route to pass through the compressor and then the indoor heat exchanger.
Describing the cooling cycle with reference to FIG. 2, the outdoor heat exchanger operates as a condenser, and the condensed refrigerant passes through the evaporator by the second three-way valve and supplies cold air to the interior of the vehicle while absorbing the ambient heat. Next, the refrigerant repeatedly passes through the circulation route to pass through the compressor and the indoor heat exchanger and again pass through the outdoor heat exchanger by the first three-way valve, thereby forming a cooling cycle.
As described above, the outdoor heat exchanger serves as a condenser in the cooling mode and serves as the evaporator in a heating mode.
In this case, the outdoor heat exchanger is preferably designed in such a manner that the number of columns of a tube for each pass decreases in accordance with the flow of the refrigerant in the cooling mode and the number of passes decreases in order to reduce the amount of pressure drop on the refrigerant side in the heating mode.
FIG. 3 illustrates the outdoor heat exchanger in which an inlet and an outlet of the refrigerant are opposite to each other when the cooling and heating modes are switched and FIG. 4 illustrates the outdoor heat exchanger in which the inlet and the outlet of the refrigerant are not changed when the cooling and heating modes are switched.
First, FIG. 3 illustrates the outdoor heat exchanger that has a 3-pass refrigerant flow in the cooling mode and has a 1-pass refrigerant flow in the heating mode.
By the way, in order to enable the refrigerant flow, baffles provided on a first header tank and a second header tank need to be configured to be closed during cooling and opened during heating.
Next, the outdoor heat exchanger of FIG. 4 is a down flow type and is configured so that the refrigerant may pass through a receiver dryer and then pass through the last pass to secure a sub-cooling region required for cooling. In general, however, the securing of the sub-cooling region as described above is limited to the cooling mode, and there is no need to secure the sub-cooling region in the heating mode in which the outdoor heat exchanger operates as the evaporator.
As illustrated in FIG. 4, in the outdoor heat exchanger, the refrigerant passes through the receiver dryer in both of the cooling and heating modes, the amount of pressure drop on the refrigerant side increases as the refrigerant passes through the receiver dryer even during heating, such that a frosting phenomenon first occurs at the last pass (portion illustrated as a dotted region in FIG. 4). Therefore, there is a need to develop an outdoor heat exchanger of a vehicle heat pump that may retard the frosting as far as possible by preventing the refrigerant from flowing to the receiver dryer during heating.